Ferrocenyl-functionalised terpyridines and their transition-metal complexes: Syntheses, structures and spectroscopic and electrochemical properties

Terpyridine ligands of the type Fc′-X-tpy′ (Fc′=ferrocenyl or octamethylferrocenyl, X=rigid spacer, tpy′=4′-substituted 2,2′:6′,2″-terpyridine) were prepared, crystallographically characterised and used for the synthesis of di- and trinuclear bis(terpyridine) complexes of RuII, FeII and ZnII. Donor–sensitiser dyads and triads based on RuII were thoroughly investigated by (spectro)electrochemistry, UV/Vis, transient absorption and luminescence spectroscopy, and an energy level scheme was derived on the basis of the data collected. Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc′ groups can occur reductively and by energy transfer. Both the redox potential of the donor Fc′ and the nature of the spacer X have a decisive influence on excited-state lifetimes and emission properties of the complexes. Some of the compounds show room-temperature luminescence, which is unprecedented for ferrocenyl-functionalised compounds of this kind.